This invention generally relates to circuit interrupter apparatus and, more particularly, to a high-voltage circuit breaker having an integral mechanism which places a closing resistance in parallel with the main contacts of the circuit breaker in a controlled reliable manner during the operation of the breaker.
As is well known in the art, when a high-voltage transmission line is closed voltage surges may be produced that exceed the insulation level of the line and thus cause destructive flashovers. Such voltage surges are suppressed by inserting a resistance of the proper value into the line in parallel with the contacts of the circuit interrupter just before the contacts the closed. Prior art circuit breakers having such closing resistor means are disclosed in U.S. Pat. Nos. 3,291,947 (Van Sickle) and 4,072,836 (Bischofberger et al.).
When interrupting very high voltages (voltages in the range of 500 kilovolts, for example), two or more interrupting units are employed in series to provide the required interrupting capacity. The use of such multiple interrupter units presents synchronizing problems when closing on an energized transmission line, particularly when closing resistors are employed for each of the interrupter units. In order for the resistors to provide the desired surge-suppression protection, it is essential that the impedance contacts of each of the interrupter units close a very short time (10 milliseconds, for example) before the closing of the circuit breaker contacts. During the opening operation of the circuit breaker, the resistors serve no function and thus should not be in the circuit. The impedance contacts are accordingly opened a few milliseconds after the interrupter contacts are closed, thereby removing the resistors from the circuit and resetting the circuit interrupter for the next cycle of operations. An integral linkage and closing resistance control assembly for automatically closing and opening the resistor contacts in the proper time sequence relative to the operation of the circuit-breaker units is disclosed and claimed in the aforementioned pending Calvino application Ser. No. 364,038.
While the unique resistor operating mechanism provided by the linkage and mechanical-timing assembly described in the aforesaid Calvino application functioned in a satisfactory manner during tests and early use in the field, it was subsequently discovered that the mechanism would occasionally fail to operate properly and permitted the circuit-breaker contacts to close without the prior insertion of the resistors into the circuit. Investigation and field test revealed that these sporadic malfunctions were caused by the random failure of the resistor operating and control mechanism to reset properly due to small variations in the "complete open" position of the circuit breaker operating linkage and mechanism. Such variations are caused by unavoidable manufacturing tolerances in the various components of the breaker and the differences in the manner in which the components are adjusted and coact with one another in a given breaker. Since resetting of the resistor control mechanism requires that a pair of apertures in a drive shaft (which is coupled to the breaker operating mechanism and breaker contacts) be perfectly aligned with matching pairs of apertures in a rotatable drive lever and free wheel cam to permit a pair of free rollers to shift position and latchingly engage the drive lever instead of the cam, even the slightest misalignment of the various paired apertures prevented the free rollers from shifting position and engaging the drive lever of the closing-resistor mechanism so that it could be rotated into reset position (along with the closing resistor contacts which are coupled to the drive lever).